Please I need help with all of these questions. 1) What is the \"molecular clock
ID: 188175 • Letter: P
Question
Please I need help with all of these questions.
1) What is the "molecular clock" theory and why is it important in establishing ancestry?
2)Describe how the effects of directional selection may be offset by immigration?
3) What is the role of natural selection in the process of evolution?
4) In humans, birth weight is an example of a characteristic affected by stabilizing selection. What does this mean to the long-term average birth weight of humans? How might the increasing number of caesarean sections by affecting this characteristic?
Explanation / Answer
1)
Molecular Clock theory holds that changes occurred in the biomolecules (DNA and Proteins) are indicative of the time they had diverged from the ancestor. We compare DNA sequence and amino acid sequences of two or more organisms and identity is taken as an index of closeness and is used to determine ancestry. However, this method is subject to conflicts, as more than one mutations at a site might have altered the site to being identical even and thus indicate closeness even when it is not.
2)
Directional selection is the selection of an extreme phenotype, say, the decrease in the size of black bears during interglacial periods in Europe. The extreme phenotype provides them with a competitive advantage and is favored by nature. However, Immigration changes the gene frequency in the population.Migration can constrain local adaptation and reduce fitness by 'migration load'. This will further push the natural selection to continue
3) Evolution stands for alteration in heritable biological characteristics of a population. Say, on an island lives birds with various size of beaks. But as we must understand long beaks will be advantageous in foraging and gradually would be selected by nature, meaning the frequency of long-beaked birds will increase given to their success in foraging. Hence they are said to be naturally selected. Hence natural selection drives evolution towards fitness, hence the Darwinian notion of -survival of the fittest'.